For air traffic moving on the ground, crossing active runways, moving on taxi ways, etc. avoiding collisions with other aircraft.
I often wondered why there are not traffic lights or illuminated signals, such as used on railroads, to tell pilots when to go, stop, and which direction to turn.
I often wondered why there are not traffic lights or illuminated signals, such as used on railroads, to tell pilots when to go, stop, and which direction to turn.